Light-emitting element

ABSTRACT

A light-emitting element comprises a light-emitting stack comprising an active layer for emitting a light; a window layer on the light-emitting stack; and a first insulative layer having a first refractive index on the window layer; wherein the first insulative layer has a first refractive index, and the window layer has a second refractive index, and a difference between the first refractive index and the second refractive index is larger than 1.5.

REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patentapplication Ser. No. 14/866,232, filed Sep. 25, 2015, which is acontinuation in-part application of U.S. patent application Ser. No.14/302,036, now U.S. Pat. No. 9,153,747, filed Jun. 11, 2014, whichclaims the right of priority based on TW application Serial No.102124862, filed on Jul. 10, 2013, the contents of which are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

The disclosure is related to a light-emitting element and moreparticularly, a light-emitting element with high reflectivity.

DESCRIPTION OF THE RELATED ART

Optical element such as LEDs are widely adopted in optical displaydevices, traffic lights, information storage apparatuses, communicationapparatuses, lighting apparatuses, and medical appliances. Theabovementioned LEDs can further connect to other devices for forming alight-emitting device. FIG. 1 illustrates a schematic structure of alight-emitting device. As shown in FIG. 1, a light-emitting device 1includes a sub-carrier 12 having a circuit 14, a soldering material 16on the sub-carrier 12 for mounting the LED 11 on the sub-carrier 12 andelectrically connecting the LED 11 with the circuit 14 of thesub-carrier 12, and an electrical connecting structure 18 forelectrically connecting with an electrode 15 of the LED 11 and thecircuit 14 of the sub-carrier 12. The abovementioned sub-carrier 12 canbe a lead frame or mounting substrate with a large size.

SUMMARY OF THE DISCLOSURE

A light-emitting element comprises a light-emitting stack comprising anactive layer for emitting a light; a window layer on the light-emittingstack; and a first insulative layer having a first refractive index onthe window layer; wherein the first insulative layer has a firstrefractive index, and the window layer has a second refractive index,and a difference between the first refractive index and the secondrefractive index is larger than 1.5.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawing is included to provide easy understanding ofthe application, and is incorporated herein and constitutes a part ofthis specification. The drawing illustrates the embodiment of theapplication and, together with the description, serves to illustrate theprinciples of the application.

FIG. 1 illustrates a schematic structure of a conventionallight-emitting device.

FIG. 2A illustrates a top view of a light-emitting element in accordancewith an embodiment of the application.

FIG. 2B illustrates a cross section of FIG. 2A along a profile line AA′in accordance with one embodiment.

FIG. 3 illustrates the percentage of the surface area of the firstcontact upper surface to a sum of surface areas of the first contactupper surface and the second contact upper surface versus power.

FIG. 4A illustrates a top view of a light-emitting element in accordancewith an embodiment of the application.

FIG. 4B illustrates a cross section of FIG. 4A along a profile line AA′in accordance with one embodiment.

FIG. 5 illustrates an exploded view of a lamp in accordance with anembodiment of the application.

DETAILED DESCRIPTION OF THE EMBODIMENTS

To better and concisely explain the application, the same name or thesame reference number given or appeared in different paragraphs orfigures along the specification should has the same or equivalentmeanings while it is once defined anywhere of the application.

The following shows the description of embodiments of the application inaccordance with the drawing.

First Embodiment

FIG. 2A illustrates a top view of a light-emitting element in accordancewith an embodiment of the application. FIG. 2B illustrates a crosssection of FIG. 2A along a profile line AA′. As shown in FIG. 2B, alight-emitting element 2 includes a substrate 20, a conducting adhesivelayer 21 on the substrate 20, a reflection structure 22 on theconducting adhesive layer 21, a transparent conducting structure 23 onthe reflection structure 22, a window layer 29 on the transparentconducting structure 23, a non-oxide insulative layer 24 between thetransparent conducting structure 23 and the window layer 29, alight-emitting stack 25 on the window layer 29, an electrical contactlayer 26 on the light-emitting stack 25, a first electrode 27 on thelight-emitting stack 25 and the electrical contact layer 26, and asecond electrode 28 below the substrate 20, wherein the light-emittingstack 25 includes a first semiconductor layer 251 between the windowlayer 29 and the first electrode 27, an active 252 between the firstsemiconductor layer 251 and the first electrode 27, and a secondsemiconductor layer 253 between the active layer 252 and the firstelectrode 27.

The first electrode 27 and/or the second electrode 28 are for anexternal voltage and made of a transparent conducting material or ametal material. The transparent conducting material includes, but is notlimited to indium tin oxide (ITO), indium oxide (InO), tin oxide (SnO),cadmium tin oxide (CTO), antimony tin oxide (ATO), aluminum zinc oxide(AZO), zinc tin oxide (ZTO), gallium zinc oxide (GZO), indium tungstenoxide (IWO), zinc oxide (ZnO), aluminum gallium arsenide (AlGaAs),gallium nitride (GaN), gallium phosphide (GaP), gallium arsenide (GaAs),gallium arsenide phosphide (GaAsP), indium zinc oxide (IZO), or diamondlike carbon (DLC). The metal material includes, but is not limited toaluminum (Al), chromium (Cr), copper (Cu), tin (Sn), gold (Au), nickel(Ni), titanium (Ti), platinum (Pt), lead (Pb), zinc (Zn), cadmium (Cd),antimony (Sb), cobalt (Co), or an alloy including the abovementioned.The first electrode 27 includes a current input portion 271 and anextension portion 272. As shown in FIG. 2A, the current input portion271 is substantially on a center of the second semiconductor layer 253,the extension portion 272 includes a first branch 2721 extends from thecurrent input portion 271 to a boundary of the light-emitting element 2,and a second branch 2722 extends from the first branch 2721 forimproving current diffusion. As shown in FIG. 2B, the extension portion272 includes a protrusive portion 273 on the electrical contact layer26, covering at least one surface of the electrical contact layer 26 forincreasing ohmic contact area with the electrical contact layer 26 andlowing resistance of the light-emitting element 2, wherein theprotrusive portion 273 higher than the current input portion 271.

The electrical contact layer 26 is between the second branch 2722 andthe light-emitting stack 25 for forming an ohmic contact between thesecond branch 2722 and the light-emitting stack 25. A resistance betweenthe electrical contact layer 26 and the second branch 2722 and aresistance between the electrical contact layer 26 and thelight-emitting stack 25 are less than a resistance between the firstelectrode 27 and the light-emitting stack 25. A material of theelectrical contact layer 26 can be a semiconductor material including atleast one element, like gallium (Ga), aluminum (Al), indium (In),phosphorus (P), nitrogen (N), zinc (Zn), cadmium (Cd), or selenium (Se).A polarity of the electrical contact layer 26 can be the same as thepolarity of the second semiconductor layer 253.

A material of the light-emitting stack 25 can be a semiconductormaterial, including more than one element like gallium (Ga), aluminum(Al), indium (In), phosphorus (P), nitrogen (N), zinc (Zn), cadmium(Cd), or selenium (Se). The polarities of the first semiconductor 251and the second semiconductor layer 253 are different for generatingelectrons or holes. A light-exiting upper surface 254 of the secondsemiconductor layer 253 can be a rough surface for reducing totalinternal reflection, so as to increase luminous efficiency of thelight-emitting element 2. The active layer 252 can emit one or morekinds of color lights which are visible or invisible and can be asingle-heterostructure, a double-heterostructure, a double sidedouble-heterostructure, multi-quantum wells structure, or quantum dots.The polarity of the window layer 29 can be the same as the polarity ofthe first semiconductor layer 251 for serving as a light extractionlayer to increase luminous efficiency of the light-emitting element 2.The window layer 29 with respect to light emitted from the active layer252 is transparent. Additionally, a material of the window layer 29 canbe a transparent conducting material including but is not limited toindium tin oxide (ITO), indium oxide (InO), tin oxide (SnO), cadmium tinoxide (CTO), antimony tin oxide (ATO), aluminum zinc oxide (AZO), zinctin oxide (ZTO), gallium zinc oxide (GZO), indium tungsten oxide (IWO),zinc oxide (ZnO), magnesium oxide (MgO), aluminum gallium arsenide(AlGaAs), gallium nitride (GaN), gallium phosphide (GaP), or indium zincoxide (IZO).

The transparent conducting structure 23 with respect to light emittedfrom the light-emitting stack 25 is transparent and can improve theohmic contact between the window layer 251 and the reflection structure22, the current conduction, and the current diffusion. Additionally, thetransparent conducting structure 23 and the reflection structure 22 canform an omni-directional reflector (ODR) which is made of a transparentmaterial including but is not limited to indium tin oxide (ITO), indiumoxide (InO), tin oxide (SnO), cadmium tin oxide (CTO), antimony tinoxide (ATO), aluminum zinc oxide (AZO), zinc tin oxide (ZTO), galliumzinc oxide (GZO), indium tungsten oxide (IWO), zinc oxide (ZnO), galliumphosphide (GaP), indium cerium oxide (ICO), indium tungsten oxide (IWO),indium titanium oxide (ITiO), indium zinc oxide (IZO), indium galliumoxide (IGO), gallium aluminum zinc oxide (GAZO), or a combinationthereof. The transparent conducting structure 23 includes a firstconducting oxide layer 230 below the non-oxide insulative layer 24 and asecond conducting oxide layer 232 between the light-emitting stack 25and the first conducting oxide layer 230. The materials of the firstconducting oxide layer 230 and the second conducting oxide layer 232 aredifferent. In another embodiment, the first conducting oxide layer 230has at least one different element in comparison with the composition ofthe material of the second conducting oxide layer 232. For example, thematerial of the first conducting oxide layer 230 is indium zinc oxide(IZO) and the material of the second conducting oxide layer 232 isindium tin oxide (ITO). The second conducting oxide layer 232 candirectly contact with the non-oxide insulative layer 24 and/or thewindow layer 29 and cover at least one surface of the non-oxideinsulative layer 24.

The transmittance of the non-oxide insulative layer 24 to the lightemitted from the light-emitting stack 25 is greater than 90% and therefractive index of the non-oxide insulative layer 24 is less than 1.4,which is better between 1.3˜1.4. A material of the non-oxide insulativelayer 24 can be a non-oxide insulative material, for example,benzocyclobutene (BCB), cyclic olefin copolymers (COC), fluorocarbonpolymer, silicon nitride (SiNx). In another embodiment, a material ofthe non-oxide insulative layer 24 can include a halide, a compound ofgroup IIA, or a compound of group VIIA, for example, calcium difluoride(CaF₂), carbon tetrafluoride (CF₄) or magnesium difluoride (MgF₂), and arefractive index of the non-oxide insulative layer 24 is less thanrefractive indexes of the window layer 29 and the transparent conductingstructure 23. Since the refractive index of the non-oxide insulativelayer 24 is less than the refractive indexes of the window layer 29 andthe transparent conducting structure 23, and a critical angle of aninterface between the window layer 29 and the non-oxide insulative layer24 is less than a critical angle of an interface between the windowlayer 29 and the transparent conducting structure 23, the probability oftotal internal reflection that occurs when the light emitted from thelight-emitting stack 25 passes through an interface between thelight-emitting stack 25 and the non-oxide insulative layer 24 isincreased accordingly. Additionally, the light that does not encountertotal internal reflection at the interface between the window layer 29and the transparent conducting structure 23 encounters totally internalreflection at the interface between the transparent conducting structure23 and the non-oxide insulative layer 24 so the light extractionefficiency of the light-emitting element 2 is increased. The transparentconducting structure 23 has a first contact upper surface 231 contactingthe window layer 29, and the non-oxide insulative layer 24 has a secondcontact upper surface 241 contacting the window layer 29. The firstcontact upper surface 231 and the second contact upper surface 241 areat the same level substantially, namely, a distance between the firstcontact upper surface 231 and the light-exiting upper surface 254 issubstantially equal to a distance between the second contact uppersurface 241 and the light-exiting upper surface 254. FIG. 3 illustratesthe percentage of the surface area of the first contact upper surface toa sum of surface areas of the first contact upper surface and the secondcontact upper surface (hereafter, surface percentage) versus power ofthe light-emitting element 2. As shown in FIG. 3, when the surface areaof the first contact upper surface 231 is about 10%˜50% of a sum of thesurface areas of the first contact upper surface 231 and the secondcontact upper surface 241, the power of the light-emitting element 2 isgreater than 50 mW, which is better than that of a light-emittingelement with a surface percentage greater than 50%. In a preferredembodiment, the surface percentage of the light-emitting element 2 is12.5˜25%, and in such case, power of the light-emitting element 2 can begreater than 55 mW. In other words, when a ratio of a surface area ofthe non-oxide insulative layer 24 to a surface area of the window layer29 is about 0.5˜0.9, the light-emitting element 2 has better powerperformance. In another embodiment, the second contact upper surface 241can be a rough surface to scatter the light from the light-emittingstack 25 for increasing luminous efficiency of the light-emittingelement 2. The non-oxide insulative layer 24 can be disposed as apattern, for example, a pattern right under the electrical contact layer26 and/or the current input portion 271 for diffusing a current. Inanother embodiment, the non-oxide insulative layer 24 can have randompattern or is not located right under the electrical contact layer 26and/or the current input portion 271. A thickness of the non-oxideinsulative layer 24 is less than a half of a thickness of thetransparent conducting structure 23. In yet another embodiment, athickness of the non-oxide insulative layer 24 is less than ⅕ of athickness of the transparent conducting structure 23 to prevent aplanarization process for the transparent conducting structure 23 fromdamaging the non-oxide insulative layer 24. At least one surface of thenon-oxide insulative layer 24 is covered by the transparent conductingstructure 23 for strongly joining the transparent conducting structure23 to the window layer 29 so as to enhance mechanical strength. Inanother embodiment, the non-oxide insulative layer 24 can directly jointhe reflection structure 22 for preventing the transparent conductingstructure 23 and the reflection structure 22 from peeling because ofinsufficient adhesion force. Additionally, the non-oxide insulativelayer 24 further includes a plurality of pores 242 penetrating thenon-oxide insulative layer 24 and the transparent conducting structure23 fills the plurality of pores 242 for forming an ohmic contact.

The reflection structure 22 can reflect light emitted from thelight-emitting stack 25, and the material of the reflection structure 22can be metal material including, but not limited to copper (Cu),aluminum (Al), tin (Sn), gold (Au), silver (Ag), lead (Pb), titanium(Ti), nickel (Ni), platinum (Pt), tungsten (W) or an alloy made of theabove mentioned. The reflection structure 22 includes a reflection layer226, a reflective adhesion layer 224 below the reflection layer 226, abarrier layer 222 below the reflective adhesion layer 224, and an ohmiccontact layer 220 below the barrier layer 222. The reflection layer 226can reflect light emitted from the light-emitting stack 25, thereflective adhesion layer 224 adheres to the reflection layer 226 andthe barrier 222, and the barrier layer 222 can prevent the material ofthe reflection layer 226 from diffusing to the ohmic contact layer 220and damaging the reflection layer 226 so as to reduce the reflectionefficiency of the reflection layer 226. The ohmic contact layer 220 hasohmic contacts with the conducting adhesive layer 21. The conductingadhesive layer 21 connects to the substrate 20 and the reflectionstructure 22 and includes a plurality of sub-layers (not shown infigures) and can be a transparent conducting material or a metalmaterial. The transparent conducting material includes, but is notlimited to indium tin oxide (ITO), indium oxide (InO), tin oxide (SnO),cadmium tin oxide (CTO), antimony tin oxide (ATO), aluminum zinc oxide(AZO), zinc tin oxide (ZTO), gallium zinc oxide (GZO), zinc oxide (ZnO),gallium phosphide (GaP), indium cerium oxide (ICO), indium tungstenoxide (IWO), indium titanium oxide (ITiO), indium zinc oxide (IZO),indium gallium oxide (IGO), gallium aluminum zinc oxide (GAZO), or acombination thereof. The metal material includes, but is not limited tocopper (Cu), aluminum (Al), tin (Sn), gold (Au), silver (Ag), lead (Pb),titanium (Ti), nickel (Ni), platinum (Pt), tungsten (W), or an alloymade of the above mentioned.

The substrate 20 can support the light-emitting stack 25 and otherlayers or structures and be made of a transparent material or aconducting material. For example, the transparent material can include,but not limited to sapphire, diamond, glass, epoxy, quartz, acryl,Al₂O₃, zinc oxide (ZnO), or aluminum nitride (AlN); the conductingmaterial can include, but be not limited to copper (Cu), aluminum (Al),molybdenum (Mo), tin (Sn), zinc (Zn), cadmium (Cd), nickel (Ni), cobalt(Co), diamond like carbon (DLC), graphite, carbon fiber, metal matrixcomposite (MMC), ceramic matrix composite (CMC), silicon (Si), zincselenide (ZnSe), gallium arsenide (GaAs), silicon carbide (SiC), galliumphosphide (GaP), gallium arsenide phosphide (GaAsP), indium phosphide(InP), LiGaO₂, or LiAlO₂.

FIG. 5 illustrates an explored view of a lamp. A lamp 4 includes a lampcover 41, a lens 42 in the lamp cover 41, a light-emitting module 44under the lens 42, a base 45 having a heat sink 46 for carrying thelight-emitting module 44, a connection portion 47, and an electricalconnector 48, wherein the connection portion 47 connects to the base 45and the electrical connector 48, and the light-emitting module 44 has acarrier 43 and a plurality of the light-emitting elements 40 of any ofthe abovementioned embodiments on the carrier 43.

Second Embodiment

FIG. 4B shows a cross section along a profile line AA′ of FIG. 4A. Asshown in FIG. 4B, a light-emitting element 100 includes a substrate 20,a conducting adhesive layer 21 on the substrate 20, a reflectionstructure 22 on the conducting adhesive layer 21, a transparentconducting structure 23 on the reflection structure 22, a window layer29 on the transparent conducting structure 23, an insulative structure 3between the transparent conducting structure 23 and the window layer 29,a light-emitting stack 25 on the window layer 29, an electrical contactlayer 26 on the light-emitting stack 25, wherein the electrical contactlayer 26 is patterned to cover a part of the light-emitting stack 25 andexposes another part of the light-emitting stack 25. A first electrode27 on the light-emitting stack 25 and the electrical contact layer 26,and a second electrode 28 below the substrate 20. The light-emittingstack 25 includes a first semiconductor layer 251, an active 252, and asecond semiconductor layer 253 sequentially on the window layer 29,wherein a part of the second semiconductor layer 253 contacts theelectrical contact layer 26 and another part of the second semiconductorlayer 253 is exposed from the electrical contact layer 26. In oneembodiment, the first electrode 27 and/or the second electrode 28 areused for die-bonding to an external device, such as a package sub-mountor a printed circuit board through a wire or a solder bump. The materialof the first electrode 27 and/or the second electrode 28 comprisestransparent conducting material, such as indium tin oxide (ITO), indiumzinc oxide (IZO), indium oxide (InO), tin oxide (SnO), cadmium tin oxide(CTO), antimony tin oxide (ATO), aluminum zinc oxide (AZO), zinc tinoxide (ZTO), gallium zinc oxide (GZO), indium tungsten oxide (IWO), zincoxide (ZnO), aluminum gallium arsenide (AlGaAs), gallium nitride (GaN),gallium phosphide (GaP), gallium arsenide (GaAs), gallium arsenidephosphide (GaAsP), diamond like carbon (DLC) and the combinationthereof, or metal, such as aluminum (Al), chromium (Cr), copper (Cu),tin (Sn), gold (Au), nickel (Ni), titanium (Ti), platinum (Pt), lead(Pb), zinc (Zn), cadmium (Cd), antimony (Sb), cobalt (Co), and thecombination thereof.

The first electrode 27 includes a current input portion 271 and anextension portion 272. As shown in FIG. 4A, the current input portion271 is substantially on a center of the second semiconductor layer 253.The extension portion 272 includes multiple first branches 2721 radiallyextending from the current input portion 271 toward a boundary of thelight-emitting element 100, and multiple second branches 2722respectively extending from the first branches 2721 and parallel to theboundary of the light-emitting element 100 for improving currentspreading over the second semiconductor layer 253. As shown in FIG. 4B,the electrical contact layer 26 is arranged as a plurality of stripeseach of which is enclosed and fully covered by each of the secondbranches 2722. The electrical contact layer 26 is formed ofsemiconductor material, such as GaAs or GaN, and the polarity of theelectrical contact layer 26 is the same as the polarity of the secondsemiconductor layer 253. The first electrode 27 comprises metal, such asAu, Ge, Ni, Ti, Pt, Al, Pd or the alloy thereof. Thus, the electricalcontact layer 26 forms an ohmic contact with the extension portion 272of the first electrode 27 for decreasing the electrical resistancebetween the extension portion 272 and the second semiconductor layer 253and lowering the forward voltage of the light-emitting element 100. Thecurrent input portion 271 and the portion of the extension portion 272not covering the electrical contact layer 26 directly contact the secondsemiconductor layer 253 and form a Schottky contact with the secondsemiconductor layer 253.

A material of the active layer 252 comprises a III-V compound material,e.g. Al_(p)Ga_(q)In_((1-p-q))P wherein 0≦p, q≦1 for emitting red,orange, yellow or amber light, or Al_(x)In_(y)Ga_((1-x-y))N wherein,0≦x, y≦1 for emitting blue, UV or green light. The polarities of thefirst semiconductor 251 and the second semiconductor layer 253 aredifferent for providing carriers, such as electrons or holes. Alight-exiting upper surface 254 of the second semiconductor layer 253not covered by the first electrode 27 is a rough surface for scatteringthe light from the light-emitting stack 25, so as to increase luminousefficiency of the light-emitting element 100. The active layer 252 canemit single or multiple colors of light and comprises asingle-heterostructure (SH), a double-heterostructure (DH), a doubleside double-heterostructure (DDH), multi-quantum wells (MQW) structure,or quantum dots. A polarity or conductivity-type of the window layer 29can be the same as that of the first semiconductor layer 251 forspreading current. The window layer 29 has a lower sheet resistance thanthe first semiconductor layer 251 and is transparent to light emittedfrom the active layer 252. Additionally, a material of the window layer29 can be a transparent conducting oxide, such as indium tin oxide(ITO), indium oxide (InO), tin oxide (SnO), cadmium tin oxide (CTO),antimony tin oxide (ATO), aluminum zinc oxide (AZO), zinc tin oxide(ZTO), gallium zinc oxide (GZO), indium tungsten oxide (IWO), zinc oxide(ZnO) and indium zinc oxide (IZO), or semiconductor material, such asaluminum gallium arsenide (AlGaAs), gallium nitride (GaN) and galliumphosphide (GaP).

The insulative structure 3 comprises a first insulative layer 31 and asecond insulative layer 32, wherein the first insulative layer 31 isformed on and contacts the window layer 29, and the second insulativelayer 32 is formed on the first insulative layer 31 and has the sameshape as the first insulative layer 31 from the top-view of thelight-emitting element 100. In the embodiment, the transmittances of thefirst insulative layer 31 and the second insulative layer 32 to thelight emitted from the active layer 252 are both greater than 90%. Therefractive index of the first insulative layer 31 is smaller than therefractive index of the window layer 29 and the refractive index of thesecond insulative layer 32. In one embodiment, the first insulativelayer 31 is made of non-oxide material including a compound of groupIIA, a compound of group IVA or a compound of group VIIA. Specifically,the non-oxide material comprises a compound with carbon-fluorine bond,such as CF₄, C₂F₆, C₃F₆, C₃F_(g), C₄F_(g), C₅F₁₂, C₆F₁₄, or otherfluorocarbon having a formula of C_(x)F_(y). Specifically, the non-oxidematerial comprises magnesium fluoride having a formula of MgF_(x), suchas MgF₂. The non-oxide material of the first insulative layer 31 has arefractive index between 1.3 and 1.4. The second insulative layer 32 ismade of oxide, such as SiO_(x), or nitride, such as SiN_(x), and has arefractive index between 1.4 and 1.8. The first insulative layer 31 andthe second insulative layer 32 are patterned to form multiple pores 242′exposing the window layer 29. When the first insulative layer 31comprises magnesium difluoride (MgF₂), the first insulative layer 31 andthe second insulative layer 32 can be patterned by lift-off process atthe same time. When the first insulative layer 31 comprises fluorocarboncompound, the first insulative layer 31 and the second insulative layer32 can be patterned by wet etching process at the same time wherein thewet-etching solution comprises buffered oxide etching solution (BOE) orhydrofluoric acid (HF). Therefore, the first insulative layer 31 and thesecond insulative layer 32 are textured to have the same patterns from atop view of the light-emitting element 100. From a top view of thelight-emitting element 100, the multiple pores 242′ are uniformlydistributed on the window layer 29 for improving the electrical currentdistribution over the window layer 29. The top-view shape of themultiple pores 242′ can be circle or polygon, such as square. As shownin FIG. 4A, the shape of each of the multiple pores 242′ is a circlewith a diameter between 2 μm and 20 μm.

Since the refractive index of the first insulative layer 31 is at least0.5 less than the refractive indexes of the window layer 29, the firstinsulative layer 31 and the window layer 29 form atotal-internal-reflection (TIR) interface to reflect the light emittedfrom the light-emitting stack 25.

The transparent conducting structure 23 has a first surface 231contacting the window layer 29, and the first insulative layer 31 has asecond surface 241 contacting the window layer 29, wherein the firstsurface 231 and the second surface 241 are substantially at the samelevel. In one embodiment, the surface area of the first surface 231 isabout 10%˜50% of a sum of the surface areas of the first surface 231 andthe second surface 241, and, in another embodiment, the surface area ofthe first surface 231 is about 12.5%˜25% of a sum of the surface areasof the first surface 231 and the second surface 241. In anotherembodiment, the second surface 241 can be a rough surface for scatteringthe light from the light-emitting stack 25 for increasing luminousefficiency of the light-emitting element 100.

In one embodiment, for a light-emitting element with an top-view arealarger than 0.25 mm², the multiple pores is preferably not overlappedthe electrical contact layer 26, or the insulative structure 3 ispreferably disposed as a pattern right under the electrical contactlayer 26 and/or the current input portion 271 for better currentspreading.

A thickness of the insulative structure 3 is between 20 nm and 2 μm orpreferably between 100 nm and 300 nm, wherein the thickness of the firstinsulative layer 31 is between 10 nm and 1 μm or preferably between 50nm and 150 nm, and the thickness of the second insulative layer 32 isalso between 10 nm and 1 μm or preferably between 50 nm and 150 nm.

The transparent conducting structure 23 includes a first conductingoxide layer 230 below the insulative structure 3 and a second conductingoxide layer 232 between the light-emitting stack 25 and the firstconducting oxide layer 230. The second conducting oxide layer 232conformably covers the insulative structure 3 and fills in the multiplepores 242 to directly contact the window layer 29. The first conductingoxide layer 230 conformably covers the second conducting oxide layer232. In the present embodiment, a thickness of the second conductingoxide layer 232 is between 1 nm and 1 μm, preferably between 10 nm and100 nm, or more preferably between 1 nm and 20 nm, and a thickness ofthe first conducting oxide layer 230 is between 1 nm and 10000 nm,preferably between 10 nm and 1000 nm or more preferably between 50 nmand 150 nm. The first conducting oxide layer 230 comprises a materialdifferent from that of the second conducting oxide layer 232. In anotherembodiment, the first conducting oxide layer 230 comprises one elementdifferent from the material of the second conducting oxide layer 232.For example, the first conducting oxide layer 230 is made of indium zincoxide (IZO), which has a refractive index between 2.0 and 2.2, and thesecond conducting oxide layer 232 is made of indium tin oxide (ITO),which has a refractive between 1.8 and 2.0. In the embodiment, therefractive index of the first conducting oxide layer 230 is larger thanthe refractive index of the second conducting oxide layer 232, therefractive index of the second conducting oxide layer 232 is larger thanthe refractive index of the second insulative layer 32, and therefractive index of the second insulative layer 32 is larger than therefractive index of the first insulative layer 31 so the refractiveindices of the first insulative layer 31, the second insulative layer32, the second conducting oxide layer 232 and the first conducting oxidelayer 230 gradually increase along the direction from the light-emittingstack toward the reflection structure 22 for reducing the probability ofoccurrence of total-internal-reflection (TIR) between the firstinsulative layer 31 and the second insulative layer 32, between thesecond insulative layer 32 and the second conducting oxide layer 232,and between the second conducting oxide layer 232 and the firstconducting oxide layer 230 for the light reflected by the reflectionstructure 22 toward the light-emitting stack 25.

In another embodiment, a thickness of the insulative structure 3 is lessthan ⅕ of a thickness of the transparent conducting structure 23 toprevent a planarization process for planarizing the transparentconducting structure 23 from damaging the insulative structure 3. Theinsulative structure 3 is substantially fully covered by the secondconducting oxide layer 232 such that the second conducting oxide layer232 provides strong adhesion force joining to the window layer 29 so asto enhance mechanical strength. In another embodiment, the transparentconducting structure 23 is omitted between the insulative structure 3and the reflection structure 22, and therefore, the insulative structure3 is directly join to the reflection structure 22 for preventing anconnecting interface of the reflection structure 22 and transparentconducting structure 23 from peeling because of poor adhesion forcebetween the insulative structure 3 and the transparent conductingstructure 23. The transparent conducting structure 23 fills the multiplepores 242 to from an ohmic contact with the window layer 29. Thetransparent conducting structure 23 is transparent to light emitted fromthe light-emitting stack 25. Additionally, the transparent conductingstructure 23 and the reflection structure 22 together form anomni-directional reflector (ODR) for perfectly reflecting the lightemitted from the light-emitting stack 25. The material of the firstconducting oxide layer 230 and the second conducting oxide layer 232comprises indium tin oxide (ITO), indium oxide (InO), tin oxide (SnO),cadmium tin oxide (CTO), antimony tin oxide (ATO), aluminum zinc oxide(AZO), zinc tin oxide (ZTO), gallium zinc oxide (GZO), indium tungstenoxide (IWO), zinc oxide (ZnO), indium cerium oxide (ICO), indiumtungsten oxide (IWO), indium titanium oxide (ITiO), indium zinc oxide(IZO), indium gallium oxide (IGO), gallium aluminum zinc oxide (GAZO),or a combination thereof. Therefore, even if the light emitted from thelight-emitting stack 25 is not reflected by thetotal-internal-reflection (TIR) interface between the first insulativelayer 31 and the window layer 29, the light can be reflected by theomni-directional reflector (ODR) made from the transparent conductingstructure 23 and the reflection structure 22 so the light extractionefficiency of the light-emitting element 100 is increased.

The reflection structure 22 has a reflectivity over 90% for the lightemitted from the light-emitting stack 25, and the material of thereflection structure 22 can be metal material including, but not limitedto copper (Cu), aluminum (Al), tin (Sn), gold (Au), silver (Ag), lead(Pb), titanium (Ti), nickel (Ni), platinum (Pt), tungsten (W) or analloy thereof. The reflection structure 22 includes a reflection layer226, an adhesion layer 224 below the reflection layer 226, a barrierlayer 222 below the adhesion layer 224, and an ohmic contact layer 220below the barrier layer 222. The reflection layer 226 can reflect lightemitted from the light-emitting stack 25. The adhesion layer 224 adheresto the reflection layer 226 and the barrier 222. The barrier layer 222can prevent the material of the reflection layer 226 from diffusing tothe ohmic contact layer 220 and lowering the reflectivity of thereflection layer 226. The ohmic contact layer 220 forms an ohmic contactwith the conducting adhesive layer 21. The conducting adhesive layer 21connects to the substrate 20 and the reflection structure 22 andincludes a plurality of sub-layers (not shown in figures), wherein theplurality of sub-layers can be made of transparent conducting materialor metal material. The transparent conducting material comprises indiumtin oxide (ITO), indium oxide (InO), tin oxide (SnO), cadmium tin oxide(CTO), antimony tin oxide (ATO), aluminum zinc oxide (AZO), zinc tinoxide (ZTO), gallium zinc oxide (GZO), zinc oxide (ZnO), galliumphosphide (GaP), indium cerium oxide (ICO), indium tungsten oxide (IWO),indium titanium oxide (ITiO), indium zinc oxide (IZO), indium galliumoxide (IGO), gallium aluminum zinc oxide (GAZO), or a combinationthereof. The metal material comprises copper (Cu), aluminum (Al), tin(Sn), gold (Au), silver (Ag), lead (Pb), titanium (Ti), nickel (Ni),platinum (Pt), tungsten (W), or an alloy made of the above mentioned.

The substrate 20 can support the light-emitting stack 25 and be made ofa conducting material. For example, the conducting material comprisesmetal, such as copper (Cu), aluminum (Al), molybdenum (Mo), tin (Sn),zinc (Zn), cadmium (Cd), nickel (Ni) and cobalt (Co), carbon compound,such as diamond like carbon (DLC), graphite and carbon fiber, composite,such as metal matrix composite (MMC), ceramic matrix composite (CMC), orsemiconductor, such as silicon (Si), zinc selenide (ZnSe), galliumarsenide (GaAs), silicon carbide (SiC), gallium phosphide (GaP), galliumarsenide phosphide (GaAsP), indium phosphide (InP), LiGaO₂ and LiAlO₂.

The principle and the efficiency of the present application illustratedby the embodiments above are not the limitation of the application. Anyperson having ordinary skill in the art can modify or change theaforementioned embodiments. Therefore, the protection range of therights in the application will be listed as the following claims.

What is claimed is:
 1. A light-emitting element, comprising: alight-emitting stack comprising an active layer for emitting a light; awindow layer on the light-emitting stack; and a first insulative layerhaving a first refractive index on the window layer; wherein the windowlayer has a second refractive index, and a difference between the firstrefractive index and the second refractive index is larger than 1.5,wherein, from a cross section of the light-emitting element, the windowlayer has a surface contacting a first surface of the first insulativelayer and a ratio of a surface area of the first surface of the firstinsulative layer to a surface area of the surface of the window layer isbetween 0.5-0.9.
 2. The light-emitting element of claim 1, wherein thefirst insulative layer comprises a compound of group IIA or a compoundof group VILA.
 3. The light-emitting element of claim 2, wherein thefirst insulative layer comprises magnesium fluoride.
 4. Thelight-emitting element of claim 1, wherein the first refractive index issmaller than the second refractive index.
 5. The light-emitting elementof claim 4, wherein the first refractive index is equal to or smallerthan 1.4.
 6. The light-emitting element of claim 1, further comprises atransparent conducting structure on the first insulative layer.
 7. Thelight-emitting element of claim 6, wherein the first insulative layercomprises multiple pores, and the transparent conducting structuredirectly contacting the surface of the window layer through the multiplepores.
 8. The light-emitting element of claim 7, wherein the transparentconducting structure having a second surface contacting the surface ofthe window layer, and a ratio of a surface area of the second surface ofthe transparent conducting structure to the surface area of the surfaceof the window layer is between 0.1250.25.
 9. The light-emitting elementof claim 6, wherein a thickness of the first insulative layer is lessthan a half of a thickness of the transparent conducting structure. 10.The light-emitting element of claim 6, wherein the transparentconducting structure comprises a first conducting oxide layer and asecond conducting oxide layer, and the second conducting oxide layer isbetween the first insulative layer and the first conducting oxide layer,and the first conducting oxide layer has a refractive index smaller thana refractive index of the second conducting oxide layer.
 11. Thelight-emitting element of claim 10, wherein the third refractive indexis between 2 and 2.2, and the fourth refractive index is between 1.8 and2.1.
 12. The light-emitting element of claim 10, wherein the secondconducting oxide layer has a thickness between 1 nm and 1 μm and thefirst conducting oxide layer has a thickness between 10 nm and 1 μm. 13.The light-emitting element of claim 7, wherein one of the multiple poreshas a length or a diameter between 2 μm and 20 μm.
 14. Thelight-emitting element of claim 7, further comprising an electricalcontact layer on the light-emitting stack opposite to the firstinsulative layer, and the electrical contact layer does not overlap themultiple pores from a top view of the light-emitting element.
 15. Thelight-emitting element of claim 7, wherein a top-view shape of one ofthe multiple pores comprises a polygon or a circle.
 16. Thelight-emitting element of claim 6, further comprising a reflectionstructure on the transparent conducting structure, a substrate on thereflection structure, and a conducting adhesive layer connecting thesubstrate to the reflection structure.